Transcript for Ryan Seacrest, Katy Perry and Lionel Richie on how this season is different
Reporter: This is "American idol." Like you've never seen it before. This is master control. This is the control room. Dim the lights and here we go. Reporter: It's just hours before "Idol" goes live, and we're behind the scenes with host Ryan Seacrest. Wow, I've never been to this set. Reporter: With millions tuning in each week, the show has launched star after star. ?????? Kelly Clarkson. Carrie Underwood! Legitimate stars. Reporter: Shattered dreams as well. Oh, Christ, that was terrible. I mean, seriously terrible. Reporter: But this season -- You couldn't get it any better. Reporter: The show is taking a very different approach, embracing positivity. Kind of evolved. We're artists. So we need encouragement. We don't need to be scared to death. When you're standing there in front of the three of us, give me a break, that's enough pressure to just shut you down. Take a deep breath and take a bow. I think about positivity. But even with that positivity, we still have a responsibility to tell the truth. You should develop a little bit more before you get into the ring. That's really important because if you lie to someone, tell them they're great when they're not yet ready, that's worse. Reporter: On this night, there's a buzz in the air. Knowing one of their biggest talents, Carrie Underwood, whom they discovered a decade ago from a tiny town in Oklahoma -- ??? because I can't make you love me ??? Reporter: Is back. I said to her when she first came to Hollywood, well, have you seen any stars since you've been here? She looked up at the sky and said, it's been pretty cloudy since I was here. When you meet -- I love Carrie Underwood. There's a realness to them. I think that's why they've become so successful. Reporter: The show ran for 15 years on fox. After a brief hiatus, ABC brought it back. How's the show changed? Well, I think the show hasn't changed terribly much, which is good. ?????? because its format is the reason it's successful. The fact that it's live in every time zone across the country and truly in realtime, so that adds to the excitement of it. Reporter: And some calling the talent -- ??? maybe I'm just like my mother ??? Reporter: Better than ever. Are you surprised year after year that there's still this much talent out there? Yes. We lose a little sleep every year wondering if we're going to have to lower the bar. But then you get to a city, then once you see magic in one place, then you find it in another. Reporter: Full of highs -- Mara. Reporter: And tearful lows. A tural-born tale, you understand? When we see the contestants in their hometown, we bring them out here, we see their growth and their evolution, it really sinks in what the promise of this franchise is. Reporter: On this night, the competitors will be cut from five down to the final three. The most difficult thing to do is to be disciplined enough not to say anything when we're on the air as I see the results coming in. Where can you see that? There's a little laptop that shows us how the votes are going. It's watching the graphs go up and down. Reporter: Just like that, Ryan rushes off to his trailer, replacing his black hoodie for a blue tailored suit. Make some noise for your top five! Reporter: Singing with their idol, Carrie Underwood, caid, gabby, Caleb, Michael, Mattie belt out "See you again." ??? Till I see you again ??? Reporter: And while they may be friends, they all want to win. Which three faces will make it into the finale? Reporter: It's time for Ryan to announce the top three singers. Caleb, gabby, Mattie. Reporter: But the journey is getting more intense. Entering into the last week of the competition. ??? Would you simply laugh at me and say ??? Reporter: For Mattie, it was a journey that came close to never even beginning. Did you ever think, I'm just going to give up trying? Every day I thought that. I tried out for other shows, didn't work. I never thought I'd do another TV show. Why did you? I just took a chance. I just thought, maybe. I'll try this. Maybe this is the way in. Reporter: Now her soulful sound and that girl next door vibe is resonating with fans and judges. You're a true artist. And it's just really exciting to you. Reporter: Country singer Caleb losing 70 pounds since first auditioning for the show. I was just at a point in my life where I was very unhappy with the way things were going. I was very close to 300 pounds. I still don't know my heaviest weight because I didn't want to get on the scale. I've taken hold of my life on all para el finalists with possibly the biggest voice. ?????? Reporter: Well, her path wasn't so clear at first either. Luke Bryan, if you recall, he wasn't a big fan of my country singing. When you try to sound country, you don't sound country. But I wanted to try to convince them that is the type of artist I want to be. And you want to win? Yes, I really do, I truly do. But the other two deserve it absolutely as much. But it is a race. There's one man going to be standing. Or one woman. You're right. One woman's going to be hopefully standing. Reporter: For "Nightline," I'm Abbie Boudreau in los Angeles.
This transcript has been automatically generated and may not be 100% accurate.